The invention relates generally to fastener installation tools and, more particularly, to an improved barrel assembly for a driver tool and a method for driving and setting fastener and plate combinations which afford superior fastener alignment and resultant improved distribution of plate stresses.
Heretofore, many diverse tools have been developed for driving a variety of fasteners into workpieces. The intended use of the driving tool often defines problems which require unique solutions. One such application requiring special driving tools is the installation of insulation on metal roof decks. The insulation is normally held to the roof deck by means of enlarged washer-like plates or discs of plastic or metal through which an elongated, threaded fastener or nail type fastener extends. These discs are often referred to as stress plates. The insulation may be six inches thick or more and, therefore, the fastener often approaches seven or eight inches, or longer, and must be held in perpendicular alignment so that it properly penetrates the insulation and the metal roof deck. In order to accomplish this feat, the elongated fastener must be loaded into the tool and a proper alignment of the fastener and the stress plate must also be achieved. Proper alignment is possible only if the setting tool provides means for holding the plate in proper relationship with the fastener.
In such environments, the loading and alignment of elongated fasteners and the handling thereof has been a constant area of concern. A number of fastener entrant means has been proposed heretofore. In my U.S. Pat. No. 3,973,605, I disclose a breach-type barrel assembly which opens in the manner of a shotgun to provide a hand fed fastener. In my U.S. Pat. No. 4,081,254, I disclose a barrel assembly in which a strip carrying fastener passes through slots in the wall of the barrel to sequentially place the fasteners within the barrel bore. Others have heretofore provided entrant means in barrel assemblies wherein the fastener is hand fed through appropriate slots in the barrel wall into the barrel bore. Exemplary of these patents are U.S. Pat. Nos. 2,845,968; 2,484,655; and Netherlands Pat. No. 51,874.
A number of power operated screwdrivers include automatic means of feeding fasteners. Exemplary of these are U.S. Pat. Nos. 3,907,014; 3,524,484; 2,922,447; and 2,327,074. Several of the above patents also teach various means such as jaw assemblies for holding the fastener in alignment at the time of installation. Other patents teaching means for holding the fastener within the barrel at the time of installation include U.S. Pat. Nos. 3,056,441; 1,889,330; and 3,226,537. In the main, the various tools disclosed in the above patents are not suitable for handling extremely long fasteners in which alignment is also critical. A commonly used tool for installing insulation on a roof deck includes a tube feed device. However, the incidents of bowed fasteners increases with fastener length and this in turn causes jamming within the tube feed. In addition, the barrel must be extremely long to accommodate a fastener fed at an angle to the barrel. Because of the required length of the barrel assemblies, the overall weight is increased. The combination of height and weight make the tool impractical to use particularly when alignment is of concern and plate-holding type of tools are necessary which require the lifting of the tool and flipping it over to be able to attach the plate to the tool.
In my U.S. Pat. No. 4,295,394, I disclose a retractable barrel assembly for an installation tool primarily intended for the installation of long fasteners through insulation and into a roof deck. The barrel assembly disclosed therein is particularly suited for installation of separate elongated fasteners and stress plates disclosed in my U.S. Pat. No. 4,361,997. In the aforementioned patent, the barrel assembly includes an entrant means for separate insertion of the elongated , fastener into the interior of the barrel bore. The entrant means is an elongated slot in the barrel wall which increases in depth along its length from a starting point and terminates in an enlarged clear through opening in registry with the bore. The retractable barrel cooperates with an inner sleeve and includes a clear through notch in registry with the elongated slot to receive the fastener in the barrel bore. A spring loaded jaw assembly is also included in a workpiece pad at the end of the barrel to slidably engage a wear plate and provide alignment for the fastener shaft as it is being driven into the hub portion of a stress plate which is held in position beneath the work pad. Pressure may be applied by a foot pad attached to the work pad. While the aforementioned barrel assembly represents a significant improvement over prior devices, there are still problems present. The jaw assemblies must be "spring" or "elastically" loaded to permit the head of the fastener to pass through the barrel. In addition, individual fasteners are sometimes lost or remain on the roof surface after the installation sequence has been completed. In such cases, the fasteners are later discovered only after the final plastic coating has been applied over the insulation resulting in an unsightly appearance and a potential site for leakage. The barrel assembly is formed in three retractable sections and is rather long and somewhat cumbersome to handle. The barrel is also moderately expensive to manufacture due to the close machining tolerances required for proper keying and slotting required for registry of parts so as to ensure trouble free insertion of the loose fasteners. True perpendicular alignment between the elongated fastener and the stress plate has also sometimes created difficulties. Thread stripping of the stress plate hub has also been a problem with this prior tool since the work pad holding the stress plate is fixed relative to the workpiece. In my U.S. Pat. No. 4,375,119, there is disclosed a floating barrel assembly which is suitable for use in conjunction with the device described in my aforementioned U.S. Pat. No. 4,295,394 to eliminate the thread stripping problem in the long barrel configuration. The subject barrel assembly, however, still requires a workpiece pad with a foot rest to ensure contact between the pad and the workpiece during the driving operation and is relatively complex in construction.
Finally depth control is also important since overdriving the fastener causes undue stress on the plates, an improperly lined fastener which is overdriven increases the likelihood of a cracked plastic plate. Even with proper aligning, overdriving can cause reverse bowing of the plate which is a potential hazard to the single ply membrane placed over the insulation. Existing tools may result in any one or more of the following: (1) reduced productivity; (2) lack of flexibility in adapting to job situation; (3) high costs and (4) maintenance problems.